Dunkleosteus, measuring up to 10 metres (33 ft) and weighing 3.6 tonnes (4.0 short tons), was a hypercarnivorous apex predator. Few other placoderms, save, perhaps, its contemporary, Titanichthys, rivaled Dunkleosteus in size.

Instead teeth, Dunkleosteus possessed two pairs of sharp gnathal plates which formed a beak. After studying a biomechanical model of the fish's jaws, scientists at the Field Museum of Natural History and the University of Chicago concluded that Dunkleosteus had the most powerful bite of any fish, With the exception of the Pliocene shark Megalodon.

Due to its heavily armoured nature, Dunkleosteus was likely a relatively slow (albeit powerful) swimmer. It is presumed to have dwelled in diverse zones of inshore waters, although it is unknown whether or not it was also somewhat pelagic, that is, swimming freely in open ocean.

Dunkleosteus had the most powerful bite of any fish, With the exception of the Pliocene shark Megalodon.

Dunkleosteus lived during the Devonian period, about 380-360 million years ago.